Long story, short: Because a crazy man, who held absolute power over the country, didn't think it a good idea.
We had our own crazies who determined that the M1 Garand had to be be 30-06 and be equipped with 8 round en block clips instead of 10 round magazines. If our general staff had not been so bone headed they would have adopted the .280 British that had half the recoil of the 06 and could have fit 10 in a clip or 12 in a magazine instead of the 8 we were forced to accept. I don't think the enemy getting shot would have much cared about the difference between .284" vs .308" in diameter. I think a lot of recoil shy people would have been better marksman with the lighter bullet. If the Germans had not been so boneheaded themselves they would have picked up on the fact that long range sniper rifles weren't much good in the hands of the average trooper in urban fighting situations. It could have been a lot worse for Europe if they had gone to the 43 earlier.
Good intentions will always be pleaded for any assumption of power. The Constitution was made to guard the people against the dangers of good intentions. There are men in all ages who mean to govern will, but they mean to govern. They promise to be good masters, but they mean to be masters.